Metrology for OLED manufacturing using photoluminescence spectroscopy

ABSTRACT

An apparatus for determining a characteristic of a photoluminescent (PL) layer comprises: a light source that generates an excitation light that includes light from the visible or near-visible spectrum; an optical assembly configured to direct the excitation light onto a PL layer; a detector that is configured to receive a PL emission generated by the PL layer in response to the excitation light interacting with the PL layer and generate a signal based on the PL emission; and a computing device coupled to the detector and configured to receive the signal from the detector and determine a characteristic of the PL layer based on the signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Indian provisional patent applicationserial number 201841014177, filed Apr. 13, 2018, which is herebyincorporated herein by reference.

BACKGROUND Field

Embodiments of the present disclosure generally relate tonon-destructive in-situ metrology for monitoring uniformity and/ordopant concentration in a layer using static and nanosecond transientphotoluminescence spectroscopy.

Description of the Related Art

Organic light-emitting diodes (OLEDs) are light-emitting diodes (LEDs)that include an organic semiconductor layer that emits light in responseto an electric current. This organic semiconductor layer, referred to asan emissive electroluminescent layer, is positioned between twoelectrodes, one of which is typically transparent (or both electrodes inthe case of transparent displays). OLEDs are used to create emissivedigital displays in devices such as television screens, computermonitors, mobile phones, hand-held game consoles, and personal digitalassistants (PDAs). The pixels of an OLED display are formed from theorganic semiconductor layers, and therefore emit visible lightthemselves. As a result, unlike a liquid crystal display (LCD), an OLEDdisplay operates without a backlight. Consequently, OLED displays aregenerally thinner and lighter than equivalent liquid crystal displays(LCDs), and produce deeper blacks and achieve higher contrast ratiosthan LCDs.

An active-matrix OLED (AMOLED) display includes a high density array oforganic electroluminescent pixels situated on a backplane that directlyaccesses and switches each individual pixel on or off. Theelectroluminescent pixels are each formed from a stack of variousorganic layers that are selectively deposited on the TFT backplane andbound by thin-film cathode and anode layers. The organic layers thatmake up each electroluminescent pixel generally include an electroninjection layer (EIL), an electron transport layer (ETL), an emissivelayer (EML), a hole transport layer (HTL), and a hole injection layer(HIL). The quality and uniformity of each of these layers cansignificantly affect the performance of the pixel and the OLED displayas a whole. For example, a variation in dopant concentration in a layeras small as a fraction of 1% can alter the dynamics of charge carriersin the layer, which in turn affects the photoluminescent behavior of thelayer. Variations in thickness of one or more of these organic layerscan also impact device efficiency.

The various organic layers of an OLED are typically formed in a singlehigh-vacuum deposition system, where each layer is deposited on thebackplane via a different chamber of the system. As a result, an OLEDdevice cannot be accessed and tested until the entire OLED formationprocess has completed, which can last up to several hours, during whicha large number of substrates are typically processed. Consequently, aprocess excursion in a single chamber can affect a large number ofdevices before being detected. Thus, such a delay in the detection ofand response to a process excursion can be costly in terms of yieldloss.

In addition, in the current state of the art, metrology techniques forOLED devices are relatively time-consuming and are employed after allorganic layers have been deposited, which can also delay detection ofprocess excursions. Further, conventional metrology techniques for OLEDdevices are generally most accurate when applied to a significantlythicker OLED layer than actual OLED device layer thickness. As a result,the signal produced when measuring the small changes associated withproduction layers of OLED devices can be inadequate for generatingreliable feedback for the deposition process.

Accordingly, there is a need in the art for systems and methods thatenable fast and accurate monitoring of the properties of the individuallayers of an OLED device.

SUMMARY

According to various embodiments, an apparatus comprises: a light sourcethat generates an excitation light that includes light from the visibleor near-visible spectrum; an optical assembly configured to direct theexcitation light onto a photoluminescent (PL) layer formed on asubstrate that is disposed in a system for depositing the PL layer; adetector that is configured to receive a PL emission generated by the PLlayer in response to the excitation light interacting with the PL layerand generate a signal based on the PL emission; and a computing devicecoupled to the detector and configured to receive the signal from thedetector and determine a characteristic of the PL layer based on thesignal.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, and may admit to other equally effective embodiments.

FIG. 1A is a schematic illustration of the various layers of a typicalorganic light-emitting diode (OLED) device.

FIG. 1B is a schematic illustration of an OLED fabrication system inwhich various embodiments of the present disclosure can be implemented.

FIG. 2 is a conceptual block diagram of an OLED layer monitoring system,according to various embodiments of the present disclosure.

FIG. 3A is an energy diagram illustrating the emission of fluorescentlight from a photoluminescent (PL) material, according to variousembodiments of the present disclosure

FIG. 3B is an energy diagram illustrating the emission of phosphorescentlight from a PL material, according to various embodiments of thepresent disclosure.

FIG. 4 is a schematic diagram illustrating an OLED monitoring system,configured according to various embodiments of the present disclosure.

FIG. 5A is a graph illustrating multiple PL intensity spectra generatedvia a static photoluminescence measurement assembly that demonstrate PLpeak intensity variation with respect to dopant concentration, accordingto an embodiment of the present disclosure.

FIG. 5B is a graph illustrating multiple PL intensity spectra generatedvia a static photoluminescence measurement assembly that demonstrate PLpeak intensity variation with respect to PL thickness, according to anembodiment of the present disclosure.

FIG. 6 is a graph illustrating a first PL intensity decay curve and asecond PL intensity decay curve generated via a transientphotoluminescence measurement assembly that demonstrate variation of PLintensity decay as a function of dopant concentration, according to anembodiment of the present disclosure.

FIG. 7 is a schematic illustration of an OLED monitoring system,configured according to various embodiments of the present disclosure.

FIG. 8 is a schematic illustration of a fiber-based OLED monitoringsystem, configured according to various embodiments of the presentdisclosure.

FIG. 9 is a schematic cross-sectional view of a probe of an array in thefiber-based OLED monitoring system of FIG. 8, according to variousembodiments of the present disclosure.

FIG. 10 is a flow chart of process steps for determining a filmcharacteristic of the PL material, according to various embodiments ofthe disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the embodiments of the presentdisclosure. However, it will be apparent to one of skill in the art thatone or more of the embodiments of the present disclosure may bepracticed without one or more of these specific details. In otherinstances, well-known features have not been described in order to avoidobscuring one or more of the embodiments of the present disclosure.

FIG. 1A is a schematic illustration of the various layers of a typicalorganic light-emitting diode (OLED) device 100. As shown, OLED device100 includes a plurality of organic semiconductor layers 120 formedbetween a cathode layer 101 and an anode layer 102. Cathode layer 101,anode layer 102, and organic semiconductor layers 120 are disposed on aglass or other substrate 103, and can each be formed via the selectivedeposition of thin films using thin film deposition techniques known inthe art. In one example, OLED device 100 is a single pixel in an OLEDdisplay.

Organic semiconductor layers 120 can include, without limitation, anelectron transport layer (ETL) 121, a hole-blocking layer (HBL) 122, anemissive layer (EML) 123, a hole transport layer (HTL) 124, and a holeinjection layer (HIL) 125, among others. Together, organic semiconductorlayers 120 provide the light-emitting functionality of OLED device 100.In FIG. 1, OLED device 100 is depicted with five organic semiconductorlayers, but in some cases OLED device 100 includes more or fewer organicsemiconductor layers. For example, organic semiconductor layers 120 mayinclude, additionally or alternatively, an electron injection layer, anelectron blocking layer, and the like.

For proper operation of OLED device 100, such as uniform color andbrightness relative to other pixels in the same OLED display, certainfilm characteristics for each of the organic semiconductor layers 120should be maintained within a specified range. Examples of suchcharacteristics include thickness and thickness uniformity of a layer,the concentration of dopant molecules within the host molecules of alayer (dopant concentration), and uniformity of the dopant concentrationacross a layer (dopant uniformity). According to various embodiments ofthe present disclosure, some or all of these film characteristics can bemeasured non-destructively after being deposited on substrate 103 whilesubstrate 103 is in-situ, in-line, and/or at end-of-line, as illustratedin FIG. 1B.

FIG. 1B is a schematic illustration of an OLED fabrication system 150 inwhich various embodiments of the present disclosure can be implemented.As shown, OLED fabrication system 150 includes multiple depositionchambers 150-1, 150-2, . . . 150N, each configured to deposit one of Ndifferent OLED layers on a substrate, such substrate 103 in FIG. 1A. Inaddition, OLED fabrication system 150 includes transfer chambers 151disposed between each of deposition chambers 150-1-150-N and a load lock152 for the removal of substrates 103. Generally, prior to removal ofsubstrates 103 and after all active layers are completed, a so-calledthe capping layer (CPL), which is not shown in FIG. 1A, is deposited onsubstrate 103. CPLs are typically transparent organic materials that aresimilar in composition to other OLED materials.

According to various embodiments of the present disclosure, certain OLEDcharacteristics can be measured non-destructively after being depositedon substrate 103 while substrate 103 is still in-situ, i.e., whilesubstrate 103 is within the deposition chamber that is forming aparticular organic semiconductor layer 120. Alternatively oradditionally, in some embodiments, certain film characteristics can bemeasured non-destructively immediately after being deposited onsubstrate 103, when substrate 103 is in-line. That is, the filmcharacteristics are measured when substrate 103 is disposed between twoof the deposition chambers of OLED fabrication system 150. For example,the in-line measurement(s) can be performed when substrate 103 isdisposed in a transfer chamber 151. Thus, in such embodiments, the filmcharacteristics for a specific semiconductor layer 120 is measurednon-destructively in real-time, after being deposited on substrate 103and before the deposition of subsequent semiconductor layers 120.Alternatively or additionally, in some embodiments, certain filmcharacteristics can be measured non-destructively when substrate 103 isat end-of-line, i.e., when deposition processes have been completed onsubstrate 103, but substrate 103 has not been removed from OLEDfabrication system 150. That is, the film characteristics are measuredwhile substrate 103 is disposed in load lock 152 or some otherend-of-line chamber of OLED fabrication system 150. In such embodiments,the film characteristics can be measured prior to deposition of a thinfilm encapsulant layer on substrate 103 and prior to exposure ofsubstrate 103 to atmosphere. In any of these situations, monitoring ofone or multiple film characteristics is performed without stopping thefabrication process. As a result, production losses associated withsystem idle time are minimized or otherwise reduced. Further, becausethe monitoring of such film characteristics can be performed immediatelyafter deposition of each organic semiconductor layer 120, process issueswith a specific deposition chamber can be detected in real time, and notafter a complete batch of substrates 103 has completed processing.

FIG. 2 is a conceptual block diagram of an OLED layer monitoring system200, according to various embodiments of the present disclosure. OLEDlayer monitoring system 200 is configured to provide in-situ andnon-destructive monitoring of dopant concentration and film thickness ofsome or all of the organic semiconductor layers 120 shown in FIG. 1. Inaddition, the measurements performed by OLED layer monitoring system 200can provide dopant concentration level and uniformity and film thicknessand its uniformity for one or more of organic semiconductor layers 120.OLED layer monitoring system 200 includes a light source 220 configuredto generate an excitation light 201, a detector 230 configured toreceive a photoluminescent (PL) emission 202, and a computing device 250coupled to detector 230. OLED layer monitoring system 200 furtherincludes an optical assembly 240 configured to direct excitation light201 to a PL layer 205 formed on a substrate 203 and to direct PLemission 202 to detector 230.

As shown, OLED layer monitoring system 200 performs one or moremeasurements on PL layer 205 while substrate 203 is disposed within adeposition system 290. Specifically, OLED layer monitoring system 200causes PL layer 205 to be excited with excitation light 201 and measuresPL emission 202 that occurs as a result of the excitation of PL layer205. Computing device 250 then determines one or more filmcharacteristics of PL layer 205 based on the measured excitation, asdescribed below. Deposition system 290 can be any technically feasiblesystem for depositing one or more PL layers 205 on substrate 203. Forexample, in some embodiments, deposition system 290 includes one or moreevacuated deposition chambers that have a low partial pressure of oxygentherein during processing. Alternatively or additionally, depositionsystem 290 includes one or more atmospheric pressure or low-vacuumdeposition chambers that can operate with an inert gas disposed therein.

PL layer 205 can be an OLED layer or any other layer of material thatemits light of a first frequency in response to excitation from light ofa second frequency that is higher than the first frequency. For example,PL layer 205 can include a layer of material that includes quantum dots,light-emitting diodes and the like. In some embodiments, PL layer 205includes an organic photo-luminescent layer.

Light source 220 can be any technically feasible light source thatgenerates a suitable excitation light 201 for exciting PL layer 205. Insome embodiments, light source 220 is configured to generate excitationlight 201 is selected in wavelength and intensity so that the chemicalproperties of PL layer 205 are not chemically altered. For example, insome embodiments, the power of excitation light 201 can be limited toavoid photo-bleaching of PL layer 205. In one such embodiment, the powerof excitation light 201 can be limited to no more than about 1 μW. Inother embodiments, the power of excitation light 201 can be varieddepending on the particular material included in PL layer 205 and theduration of exposure of PL layer 205 to excitation light 201. Thus, insome embodiments, the power of excitation light 201 can as much as about10 μW.

In some embodiments, light source 220 includes one or more lasers thateach generate a specific excitation light 201 for a particular PL layer205, so that the particular PL layer 205 can be excited by theappropriate specific excitation light. For example, in such embodiments,light source 220 may include a tunable laser that selectively generatesa first wavelength light (e.g., 405 nm light) for exciting a first PLlayer 205 and a second wavelength light (e.g., 375 nm light) forexciting a second PL layer 205. Alternatively or additionally, in suchembodiments, light source 220 may include multiple lasers that are eachemployed for generating excitation light 201 for a different PL layer205. In some embodiments, light source 220 includes a broadband lightsource, such as a white plasma-based light source, a whitelight-emitting diode (LED), or some other light source that generateslight in the 350-400 nm wavelength range. In some embodiments, lightsource 220 is a single light source that is employed to generateexcitation light 201 having the same frequency for the excitation of anyPL layer 205 that is measured by OLED layer monitoring system 200. Forexample, in such an embodiment, light source 220 includes a laser thatgenerates an excitation light 201 having a single fixed frequency oflight or a single fixed range of frequencies of light between about 300nm and about 450 nm.

For clarity, in the embodiment illustrated in FIG. 2, excitation light201 is depicted to be incident on PL layer 205 at a non-normal angle ofincidence 209. In other embodiments, angle of incidence 209 can be 90°,or any other suitable angle for a particular configuration of OLED layermonitoring system 200,

Detector 230 is configured to receive PL emission 202 when PL layer 205is excited by excitation light 201, and can include any suitable lightdetector. As will be discussed further below, the PL emission 202 willhave a different set of wavelengths from the one or more wavelengthsfound in excitation light 201. For example, in some embodimentscomputing device 250 employs a spectral intensity of PL emission 202 todetermine one or more film characteristics of PL layer 205. In suchembodiments, detector 230 includes a spectrometer configured to quantifya radiant intensity for each of a plurality of wavelengths of lightincluded in PL emission 202. In such embodiments, the spectrometergenerally includes a grating and/or other optical elements to spatiallydisperse the various frequencies of light included in PL emission 202.In addition, a suitable detector is optically coupled to or included inthe spectrometer, such as an array of photodetectors or charge-coupleddevices (CODs) that each quantify a PL intensity for a different portionof the spectrum of PL emission 202. Thus, the spectrally dispersed PLlight is imaged by the CCD image sensor pixels at the focal plane of thespectrometer where the CCD image sensor is located. The CCD pixels arecalibrated for the wavelength range with a suitable calibration lampsuch that each pixel represents a specific wavelength and the PLspectrum can be directly recorded on the CCD sensor.

Alternatively or additionally, in some embodiments, computing device 250employs a single intensity value associated with PL emission 202 todetermine one or more film characteristics of PL layer 205. In suchembodiments, detector 230 includes a suitable device for quantifyingincident light intensity, such as a photomultiplier tube orphoton-counters. In such embodiments, detector 230 may further includean optical filter or other optical element configured to selectivelytransmit light of a specified wavelength or wavelength band, so thatlight detected by detector 230 is limited to the specified wavelength orwavelength band.

Computing device 250 includes logic configured to receive signals fromdetector 230 and to determine one or more film characteristics of one ormultiple PL layers 205 formed on substrate 203. Computing device 250 canbe any computing device suitable for practicing one or more embodimentsof the present disclosure. Computing device 250 may be implemented as acentral processing unit (CPU), a graphics processing unit (GPU), anapplication-specific integrated circuit (ASIC), a field programmablegate array (FPGA), any other type of processing unit, or a combinationof different processing units, such as a CPU configured to operate inconjunction with a GPU. In general, computing device 250 may be anytechnically feasible hardware unit capable of processing data and/orexecuting software applications for implementing one or more embodimentsof the present disclosure. Further, computing device 250 may correspondto a physical computing system, or may be a virtual computing instanceexecuting within a computing cloud. In some embodiments, thefunctionality of computing device 250 is incorporated into depositionsystem 290.

In some embodiments, computing device 250 determines a dopantconcentration of PL layer 205 by measuring a transient photoluminescenceof PL layer 205 and comparing the measured transient photoluminescenceto a previously established calibration curve, table, or function. Asdescribed below, transient photoluminescence in organic semiconductorlayers is a function of dopant concentration, and is generallyunaffected by thickness of the organic semiconductor layer. Transientphotoluminescence (TPL) of an organic semiconductor layer is generallydetermined by measuring the decay over time of the photoluminescenceintensity, at one or more wavelengths, generated by exposing a portionof an organic semiconductor layer to an amount of radiation generated bya light source (e.g., pulse of the excitation light 201). In TPL, thephotoluminescence spectrum is monitored as a function of delay betweenexcitation pulse and CCD gate pulse that records the PL intensity. Thekinetics of PL decay is indicative of the outflow of excitation energy,which in turn is indicative of the host:dopant ratio in the emissivelayer. In the emissive layer, the host molecular system is excited,which in turn transfers the excitation energy via intersystem crossingover to the excited dopant molecular system. Subsequently, the exciteddopant relaxes to the ground state, releasing energy in form ofphotoluminescence. Hence, the larger the dopant concentration, thefaster the PL decay, which is what is observed in the TPL monitoringsystem described herein. The PL decay kinetics are independent of layerthickness but very sensitive to the host:dopant ratio in the emissivelayer.

In some embodiments, computing device 250 determines a dopingconcentration of PL layer 205 by performing a thickness measurement (forexample via reflectometry) and measuring a static photoluminescence ofPL layer 205. Based on the thickness measurement and the staticphotoluminescence measurement, computing device 250 then determines thedopant concentration. Specifically, computing device 250 can determinethe dopant concentration of PL layer 205 by comparing the measuredstatic photoluminescence to a previously established calibration curve,table, or function that is associated with the measured thickness of aparticular PL layer 205. Thus, even though the static photoluminescenceof PL layer 205 is a function of both the thickness of PL layer 205 andthe concentration of dopant included in PL layer 205, computing device250 can determine a thickness of PL layer 205 by measuring staticphotoluminescence of PL layer 205.

Alternatively or additionally, in some embodiments, computing device 250determines a thickness of PL layer 205 by measuring a transientphotoluminescence of PL layer 205 and a static photoluminescence of PLlayer 205. In such embodiments, computing device 250 first determines adopant concentration of PL layer 205 by measuring a transientphotoluminescence of PL layer 205 and comparing the measuredphotoluminescence to a first calibration curve, table, or function.Computing device 250 then determines a thickness of PL layer 205 bymeasuring a static photoluminescence of PL layer 205 and comparing themeasured static photoluminescence to a second calibration curve, table,or function for the dopant concentration of PL layer 205 that isdetermined based on transient photoluminescence.

As noted above, optical assembly 240 is configured to direct excitationlight 201 to PL layer 205 and to direct PL emission 202 to detector 230.Optical assembly 240 can include any of various configurations,depending on the which film characteristic or characteristics of PLlayer 205 are determined by computing device 250. The configuration ofoptical assembly can also depend on which information associated with PLemission 202 is employed by computing device 250 to determine the filmcharacteristic or characteristics of PL layer 205.

As noted above, PL emission 202 is generated by PL layer 205 whenexcitation light 201 is incident on PL layer 205. More specifically,atoms within a host material of PL layer 205 and/or a dopant material inPL layer 205 contribute to the generation of PL emission 202. The hostmaterial of PL layer 205 can include any PL material, which is amaterial that emits light by photoexcitation, i.e. in response to theabsorption of photons. For example, the organic semiconductors includedin OLED devices are typically PL materials. Examples of such host PLmaterials include CBP (4,4′-Bis(N-carbazolyl)-1,1′-Biphenyl), TCTA(4,4′,4″-Tris(carbazole-9-yl)triphenylamine) or TPBi(2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)).Examples of dopant materials that can be included in PL layer 305include green emitter molecules like Ir(ppy)₂(acac)(Bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III)) (greenemitter), red emitter molecules like Ir(btpy)₃(Tris(2-(benzo[b]thiphen-2-yl)pyridineiridium(III)) and blue emittermolecules like Bebq2 (Bis(10-hydroxybenzo[h]quinolinato)beryllium). PLemission 202 can include photons emitted via fluorescence,phosphorescence, or a combination of both, as illustrated in FIGS. 3Aand 3B.

FIG. 3A is an energy diagram illustrating the emission of fluorescentlight 301 from a fluorescent material, and FIG. 3B is an energy diagramillustrating the emission of phosphorescent light 302 from aphosphorescent material, according to various embodiments of the presentdisclosure. As shown in FIG. 3A, the emission of fluorescent light 301(i.e., fluorescence) occurs from vibrational state v₀ of excited singletS₁ down to S₀ (and its vibrational levels). When absorption 311 ofincident light 312 that exceeds the bandgap of the PL material(typically in the visible to ultra-violet range) occurs, electrons inthe PL material are excited to higher vibrational states of S₁. Theseexcited vibrational energy states relax via non-radiative transfer 313to the ground vibrational state of S₁. Eventually the molecules of thePL material relax 314 to a ground electronic state S₀, emittingfluorescent light 301. Usually fluorescence occurs at a wavelength thatis significantly red-shifted from the excitation wavelength (Stokesshift), and is unique for every fluorescent material. Typicalfluorescence lifetimes range between femtoseconds (fs) to picoseconds(ps).

As shown in FIG. 3B, the emission of phosphorescent light 302 (i.e.,phosphorescence) occurs from higher triplet state (T₁) to singlet groundstate (S₀) after the singlet excitation undergoes the inter-systemcrossing 321 from higher singlet (S₁) of the host PL material to thehigher triplet state (T₁) of a dopant material within the PL material.Relaxation 322 of molecules from T₁ to S₀ emits Stokes' shifted photonscollectively known as phosphorescence (phosphorescent light 302). Thedecay lifetimes are very long ranging anywhere between nanoseconds (ns)to milliseconds (ms) and even hours, depending on the PL material andsurrounding conditions. As employed herein, the term “photoluminescence”is a collective term for material emission processes that includefluorescence, phosphorescence, or a combination of both. Thus, PLemission 202 of FIG. 2 can include fluorescent light 301, phosphorescentlight 302, or a combination of both.

It is noted that incident light 312 generally includes a firstwavelength or group of wavelengths, while fluorescent light 301 includesa second wavelength or group of wavelengths that is different from thefirst wavelength or group of wavelengths. Similarly, phosphorescentlight 302 includes a third wavelength or group of wavelengths that isdifferent from the first wavelength or group of wavelengths. Thus, whilethe energy that causes the generation of PL emission 202 originates fromexcitation light 201, the light making up PL emission 202 includesdifferent photons at different energies than the photons of excitationlight 201.

According to some embodiments, excitation light 201 includes light inthe visible light spectrum, i.e., light of wavelengths from about 400 nmto about 700 nm. According to some embodiments, excitation light 201includes light in the near-infrared spectrum, which includes light ofwavelengths from about 700 nm to about 800 nm. According to someembodiments, excitation light 201 includes light in the mid-infraredspectrum, which includes light of wavelengths from about 800 nm to about3000 nm (3 microns). According to some embodiments, excitation light 201includes light in the near ultraviolet spectrum, which includes light ofwavelengths from about 100 nm to about 400 nm. It is noted that X-raysare generally considered to include light of wavelengths of about 0.01nm to about 10 nm, and which does not overlap with the wavelengths oflight in the near ultraviolet spectrum. Thus, unlike analyticaltechniques that employ X-rays to generate fluorescent emissions, such asX-ray fluorescence (XRF), embodiments described herein employ much lessenergetic photons to generate PL emission 202. In some embodiments, PLemission 202 includes light having a wavelength in the visible spectrum.Alternatively or additionally, in some embodiments, PL emission 202includes light having a wavelength in the near infra-red spectrum and/orthe mid-infrared spectrum. In some embodiments, PL emission 202 includeslight having a wavelength in the near-visible spectrum, which caninclude light from the near infra-red spectrum to the near ultravioletspectrum.

In some embodiments, an OLED monitoring system is configured todetermine one or more film characteristics of a PL layer by measuringboth static photoluminescence and/or transient photoluminescence of a PLmaterial. One such embodiment is illustrated in FIG. 4. FIG. 4 is aschematic diagram illustrating an OLED monitoring system 400, configuredaccording to various embodiments of the present disclosure. OLED layermonitoring system 400 includes a laser 401, a laser electronicsynchronization module 402, a static photoluminescence measurementassembly 420 that acts as a first detector, and a transientphotoluminescence measurement assembly 430 that acts as a seconddetector. In some embodiments, OLED layer monitoring system 400 furtherincludes an optical assembly 440 that directs the excitation light 201and PL emission 202 as shown. Optical assembly 440 can includefree-space optical elements, such as a beam splitter 441 and mirror 442,and/or fiber optic elements (not shown). OLED layer monitoring system400 typically also includes a computing device for receiving signalsfrom static photoluminescence measurement assembly 420 and transientphotoluminescence measurement assembly 430 and for determining one ormore film characteristics of PL layer 205. For clarity, the computingdevice of OLED layer monitoring system 400 is omitted in FIG. 4.

Laser 401 is a laser configured to generate timed pulses on a time scalethat corresponds to the PL decay period of PL layer 205 when excited bya suitable frequency of incident light. For example, in someembodiments, laser 401 is configured to generate timed pulses on thepicoseconds (ps) timescale. Laser electronic synchronization module 402synchronizes the output of laser 401 with the data collection of staticphotoluminescence measurement assembly 420 and transientphotoluminescence measurement assembly 430.

Static photoluminescence measurement assembly 420 is configured tomeasure steady-state photoluminescence of PL layer 205 when PL layer 205is excited by laser 401. In embodiments in which PL layer 205 is excitedby laser 401, laser 401 can operate either as a continuous-wave (CW)laser or pulsed laser. In some embodiments, static photoluminescencemeasurement assembly 420 is configured to measure spectral informationassociated with PL emission 202. In such embodiments, staticphotoluminescence measurement assembly 420 includes a spectrometer 421for spatially separating the frequencies of PL emission 202 and a lightdetector 422 for quantifying the radiant intensity for each wavelengthof interest in PL emission 202. Alternatively, spectrometer 421 can bereplaced by any suitable optical element or elements that spatiallydisperse the various frequencies of light included in PL emission 202.In some embodiments, light detector 422 includes an array of lightdetectors, such as a CCD array or CMOS array, where each light detectorin the array measures a radiant intensity for a particular wavelength orwavelength band of interest. Thus, in operation, staticphotoluminescence measurement assembly 420 generates an intensityspectrum of PL emission 202 that facilitates measurement of one or morefilm characteristics of PL layer 205. Examples of such PL intensityspectra are illustrated in FIGS. 5A and 5B.

FIG. 5A is a graph 500 illustrating multiple PL intensity spectra501-503 generated via static photoluminescence measurement assembly 420that demonstrate PL peak intensity variation with respect to dopantconcentration, according to an embodiment of the present disclosure.Each of PL intensity spectra 501-503 is generated for a different 50 nmthick PL layer 205 of Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) thatcontains the dopant Ir(ppy)₂(acac). Specifically, PL intensity spectrum501 is generated for a TCTA layer that includes 1% Ir(ppy)₂(acac), PLintensity spectrum 502 is generated for a TCTA layer that includes 3%Ir(ppy)₂ (acac); and PL intensity spectrum 503 is generated for a TCTAlayer that includes 7% Ir(ppy)₂(acac). As shown, the magnitude of peakintensities 501A, 502A, and 503A varies as a function of dopantconcentration, where increasing dopant concentration in the TCTA layerresults in an increase in the magnitude of peak intensity. Specifically,in the embodiment illustrated in FIG. 5A, the magnitude of peakintensities 501A, 502A, and 503A are 186279±2.7%, 198084±2.9%, and211718±1.9%, respectively. In addition, the peak wavelength of PLintensity spectra 501-503 increases (i.e., red-shifts) with increasingdopant concentration. Specifically, in the embodiment illustrated inFIG. 5A, the peak wavelengths of PL intensity spectra 501-503 are 517.89nm, 518.20 nm, and 520.69 nm, respectively.

Thus, in some embodiments, for a known thickness of PL layer 205 of aparticular PL material, a PL intensity spectrum generated by staticphotoluminescence measurement assembly 420 can indicate theconcentration of dopant included in PL layer 205. In such embodiments, acomputing device of OLED layer monitoring system 400 compares a PLintensity spectrum for the PL layer 205 of known thickness to previouslyestablished calibration curves for that thickness of PL layer 205 anddetermines the concentration of dopant in the PL layer 205 of knownthickness. Alternatively or additionally, the computing device of OLEDlayer monitoring system 400 can determine a specific value from the PLintensity spectrum for the PL layer 205 of known thickness, such as amagnitude of the peak intensity of the PL intensity spectrum and/or awavelength of the peak intensity of the PL intensity spectrum. Thecomputing device then compares the specific value or values to apreviously established calibration table or function to determine theconcentration of dopant in the PL layer 205 of a known thickness. It isnoted that for each particular thickness and particular PL material, adifferent calibration process is typically employed for determining theconcentration of dopant included in PL layer 205.

Conversely, when PL layer 205 includes a known concentration of dopant,a PL intensity spectrum generated by static photoluminescencemeasurement assembly 420 enables the computing device of OLED layermonitoring system 400 to determine the thickness of PL layer 205 usingcalibration curves, tables, or functions in a similar fashion. Forexample, FIG. 5B is a graph 550 illustrating multiple PL intensityspectra 551-553 generated via static photoluminescence measurementassembly 420 that demonstrate PL peak intensity variation with respectto PL thickness, according to an embodiment of the present disclosure.Each of PL intensity spectra 551-553 is generated for a respective PLlayer 205 of a different thickness ofTris(8-hydroxyquinoline)aluminum(III), commonly known as AlQ3.Specifically, PL intensity spectrum 551 is generated for a first AlQ3layer that is 10 nm thick, PL intensity spectrum 552 is generated for asecond AlQ3 layer that is 30 nm thick, and PL intensity spectrum 553 isgenerated for a third AlQ3 layer that is 50 nm thick, where the first,second, and third layers each have the same dopant concentration. Asshown, the magnitude of the peak intensities of PL intensity spectra551-553 varies significantly as a function of dopant concentration.

Returning to FIG. 4, transient photoluminescence measurement assembly430 is configured to measure transient photoluminescence of PL layer 205when PL layer 205 is excited by laser 401. In some embodiments,transient photoluminescence measurement assembly 430 is configured tomeasure PL intensity information associated with PL emission 202 viatime-correlated single photon counting (TCSPC). In TCSPC, thetime-dependent intensity profile of PL emission 202 is recorded in thetime domain when PL emission 202 occurs upon excitation by a short flashof light, such as a laser pulse from laser 401. In such embodiments,transient photoluminescence measurement assembly 430 includes a lightdetector 431 that is configured for the precisely timed registration ofsingle photons of PL emission 202. For example, in some embodiments,light detector 431 includes a single-photon sensitive detector, such asa photomultiplier tube (PMT), a micro channel plate (MCP), a singlephoton avalanche diode (SPAD), or a hybrid PMT. For sufficientsensitivity in measuring the time decay of PL emission 202, in someembodiments, the measurements of PL emission 202 by light detector 431are based on precisely times repetitive excitations of PL layer 205. Thereference for the timing of the excitations and associated measurementscan be the corresponding excitation pulse, which is provided by laserelectronic synchronization module 402. In operation, transientphotoluminescence measurement assembly 430 generates a PL intensitydecay curve that facilitates measurement of one or more filmcharacteristics of PL layer 205. Examples of such PL intensity decaycurves are illustrated in FIG. 6.

FIG. 6 is a graph 600 illustrating a first PL intensity decay curve 601and a second PL intensity decay curve 602 generated via transientphotoluminescence measurement assembly 430 that demonstrate variation ofPL intensity decay as a function of dopant concentration, according toan embodiment of the present disclosure. First PL intensity decay curve601 and second PL intensity decay curve 602 are each generated for adifferent 50 nm thick PL layer 205 of TCTA that contains the dopant(ppy)₂Ir(acac). Specifically, first PL intensity decay curve 601 isgenerated for a PL layer 205 that includes 5% (ppy)₂Ir(acac) and secondPL intensity decay curve 602 is generated for a PL layer 205 thatincludes 7% (ppy)₂Ir(acac). The PL intensity counts (Y-axis of graph600) are shown in arbitrary units, and depict the discrete intensitiesof light, such as counts, measured over time after PL layer 205 isexcited by excitation light 201.

In contrast to the PL intensity spectra 501-503 of FIG. 5, in theembodiment illustrated in FIG. 6, each data point is based on a numberof photons measured by transient photoluminescence measurement assembly430 over a single band of wavelengths, such as 520-530 nm (greenemitters) or 620-630 nm (red emitters). That is, spectral dispersion ofPL emission 202 is not performed, and photons within a predeterminedrange of wavelengths of PL emission 202 are measured. To that end, insome embodiments, transient photoluminescence measurement assembly 430also includes an optical filter 432 that is configured to limit thewavelengths of PL emission 202 received by transient photoluminescencemeasurement assembly 430 to the predetermined range of wavelengths. Ingeneral, the predetermined range of wavelengths that is sampled bytransient photoluminescence measurement assembly 430 is a relativelywide band compared to each of the wavelength bands associated with eachdata point in the PL intensity spectra 501-503 of FIG. 5. Furthermore,the predetermined range of wavelengths sampled by transientphotoluminescence measurement assembly 430 can be selected based on thehost material and/or dopant material of PL layer 205.

As illustrated by first PL intensity decay curve 601 and second PLintensity decay curve 602, the decay over time of the intensity of PLemission 202 after a discrete excitation by incident light varies as afunction of dopant concentration, but not thickness of PL layer 205.That is, increasing dopant concentration in PL layer 205 results in anincrease in the rate of decay of PL emission 202, while a change inthickness of PL layer 205 has no significant effect on the rate of decayof PL emission 202. As a result, in some embodiments, a PL intensitydecay curve generated by transient photoluminescence measurementassembly 430 can indicate the concentration of dopant included in PLlayer 205. In such embodiments, PL intensity values are collected atdifferent times after a triggering laser pulse from laser 401 excites aPL layer 205 that includes a particular host material and dopantmaterial. The computing device of OLED layer monitoring system 400 thenconstructs a PL intensity curve similar to first PL intensity decaycurve 601 or second PL intensity decay curve 602, and compares theconstructed PL intensity decay curve to previously establishedcalibration curves for a similar PL layer 205. Based on the comparison,the computing device determines dopant concentration in PL layer 205. Insuch embodiments, any suitable curve-fitting algorithm can be employedby the computing device to determine dopant concentration in PL layer205.

In one such embodiment, the computing device of OLED layer monitoringsystem 400 can determine a value for a fitting parameter for the PLintensity decay curve constructed for a PL layer 205. The computingdevice then determines a dopant concentration of PL layer 205 based onthat specific value of the fitting parameter. For example, the computingdevice can determine a dopant concentration by comparing the specificvalue of the fitting parameter to a calibration table of previouslyestablished values for the fitting parameter that is generated using PLlayers having a known dopant concentration. In such an embodiment, adouble-exponent fitting equation, such as Equation 1, can be employed todetermine a PL intensity decay curve for a known dopant concentrationthat most closely matches the PL intensity decay curve constructed forPL layer 205.

$\begin{matrix}{Y = {Y_{0} + {A_{1}\exp\left\{ \frac{- \left( {x - x_{0}} \right)}{\tau_{1}} \right\}} + {A_{2}\exp\left\{ \frac{- \left( {x - x_{0}} \right)}{\tau_{2}} \right\}}}} & (1)\end{matrix}$

In equation 1, Y0 is a y-axis (PL count) offset, X0 is a x-axis(timedelay) constant, and A₁, A₂, τ₁, and τ₂ are additional fittingparameters. In embodiments in which Equation 1 is employed to determinea dopant concentration of PL layer 205, T₂ can be selected as thefitting parameter that is compared to known calibration values. Forexample, in the embodiment illustrated in FIG. 6, for intensity decaycurve 601, A₁=2137, A₂=2568, τ₁=220 ps and τ₂=1.04 ns, whereas forintensity decay curve 602 A₁=3693, A₂=1506, τ₁=135.6 ps, and τ₂=1.15 ns

In some embodiments, an OLED monitoring system includes free-spaceoptical elements for directing excitation light from a light source to aPL layer, and for directing a PL emission from the PL layer to one ormore detectors. One such embodiment is illustrated in FIG. 7. FIG. 7 isa schematic illustration of an OLED monitoring system 700, configuredaccording to various embodiments of the present disclosure. OLEDmonitoring system 700 includes one or more free-space optical elementsthat interact with and/or direct excitation light 201, PL emission 202,or both excitation light 201 and PL emission 202.

For example, in some embodiments, OLED monitoring system 700 includesone or more filters 701, such as a neutral-density filter or otheroptical filter for modifying the intensity or color distribution ofexcitation light 201. In some embodiments, OLED monitoring system 700includes one or more lenses 702 to shape and/or focus excitation light201. In some embodiments, OLED monitoring system 700 includes a dichroicmirror 703 that is highly reflective for wavelengths associated withexcitation light 201 (e.g., on the order of about 400 nm) and highlytransmissive for wavelengths associated with PL emission 202 (e.g., onthe order of about 600 nm). In some embodiments, OLED monitoring system700 includes an objective lens 704 configured to focus excitation light201 onto a measuring location 720 on PL layer 205. In such embodiments,objective lens 704 may also be configured to focus PL emission 202 ontostatic PL measurement assembly 420 and/or transient PL measurementassembly 430. In some embodiments, OLED monitoring system 700 includes aconfocal pinhole 705 that is configured to block out-of-focus excitationlight 201 and is positioned between objective lens 704 and laser 401. Insome embodiments, OLED monitoring system 700 includes a filter 706, suchas a notch filter, configured to stop unwanted frequencies of light fromreaching static PL measurement assembly 420 and/or transient PLmeasurement assembly 430, such as frequencies associated with excitationlight 201. In some embodiments, OLED monitoring system 700 includes abeam-splitter 707 configured to direct a portion of PL emission 202 tostatic PL measurement assembly 420 and a portion of PL emission 202 totransient PL measurement assembly 430. In some embodiments, OLEDmonitoring system 700 includes static PL measurement assembly 420 and/ortransient PL measurement assembly 430.

In some embodiments, OLED monitoring system 700 includes additionaloptical elements or fewer optical elements than those depicted in FIG.7. Further, in some embodiments, one or more of the free-space opticalelements depicted in FIG. 7 can be replaced with one or more fiber-basedcomponents of substantially equivalent functionality.

In some embodiments, OLED monitoring system 700 controls or iscommunicatively connected to a movable stage 710 for translatingsubstrate 203 relative to objective lens 704. In such embodiments,movable stage 710 is configured to translate substrate 203 in adirection perpendicular to the direction of incident excitation light201. In such embodiments, stage 710 is configured to translatehorizontally, i.e., in the direction indicated by arrow 711, orvertically, i.e., out of the page in FIG. 7. In some embodiments,movable stage 710 is an X-Y stage configured to translate substrate 203both horizontally and vertically, so that excitation light 201 can bedirected to a plurality of measurement locations 720 that aredistributed in two dimensions on PL layer 205. Alternatively oradditionally, in some embodiments, movable state 710 is furtherconfigured with additional motion capability, such as Z-motion (which isperpendicular to X- and Y-motion) and rotational motion, for example tooffset correction of focal length sensitivity.

In some embodiments, movable stage 710 is disposed within the processchamber that has deposited PL layer 205. In one such embodiment, movablestage 710 is disposed within the deposition chamber that has depositedPL layer 205, and measurements of PL layer 205 are performed beforesubstrate 203 is removed from the deposition chamber. In anotherembodiment, movable stage 710 is disposed within the deposition systembut outside the deposition chamber that has deposited PL layer 205. Forexample, movable stage 710 can be disposed within a transfer chamber ofthe deposition system, and measurements of PL layer 205 are performedafter substrate 203 is removed from the deposition chamber that hasdeposited PL layer 205.

In the embodiment illustrated in FIG. 7, OLED monitoring system 700directs excitation light 201 to a single measuring location 720 on PLlayer 205. In other embodiments, when substrate 203 is in a particularposition relative to OLED monitoring system 700, OLED monitoring system700 is configured to direct excitation light 201 to multiple measuringlocations 720 on PL layer 205. For example, in one such embodiment, OLEDmonitoring system 700 includes a linear array of N objective lenses 704that extends out of the page. Thus, OLED monitoring system 700 isconfigured to direct excitation light 201 to N locations on PL layer 205without repositioning substrate 203. As a result, PL emission 202 can begenerated at the N locations on PL layer 205 and measured by staticphotoluminescence measurement assembly 420 and/or transientphotoluminescence measurement assembly 430 without repositioning movablestage 710. In such an embodiment, movable stage 710 is typicallyconfigured to translate substrate 203 along a single directionperpendicular to the direction of incident excitation light 201, i.e.,either vertically or horizontally.

In some embodiments, an OLED monitoring system includes one or moreoptical-fiber-based components. One such embodiment is illustrated inFIG. 8. FIG. 8 is a schematic illustration of a fiber-based OLEDmonitoring system 800, configured according to various embodiments ofthe present disclosure. OLED monitoring system 800 includes one or moreoptical-fiber-based components that interact with and/or directexcitation light 201, PL emission 202, or both excitation light 201 andPL emission 202.

In some embodiments, OLED monitoring system 800 includes an array 810that includes a plurality of probes 821. Each of probes 821 is coupledto a fiber optic splitter 802 via a fiber bundle 822, where each fiberbundle 822 includes at least one fiber (not shown) for directingexcitation light 201 to a probe 821 and at least one fiber (not shown)for directing PL emission 202 from the probe 821. In addition, fiberoptic splitter 802 is coupled to laser 401 via an optical fiber 823 anda PL measurement assembly 830 via an optical fiber 824. Thus, each ofprobes 821 is coupled to laser 401 and PL measurement assembly 830 viafiber optic splitter 802 and various optical fibers. In someembodiments, PL measurement assembly 830 includes the functionality ofstatic PL measurement assembly 420, transient PL measurement assembly430, or a combination of both.

Each of probes 821 is configured to direct excitation light 201 to aparticular measurement location 803 on substrate 203. In addition, eachof probes 821 is configured to receive PL emission 202 and transmit PLemission 202 to PL measurement assembly 830 via fiber optic splitter802.

In the embodiment illustrated in FIG. 8, array 810 is a linear arraythat is configured to facilitate PL measurements from one edge ofsubstrate 203 (e.g., a top edge 804) to an opposing edge of substrate203 (e.g., a bottom edge 805) without repositioning substrate 203 viamovable stage 710. In other embodiments, array 810 extends across aportion of substrate 203 rather than from top edge 804 to bottom edge805. In some embodiments, array 810 is a two-dimensional array of probes821 rather than a linear array of probes. Furthermore, in someembodiments, array 810 is disposed within a vacuum chamber of thedeposition system that deposits one or more PL layers on substrate 203.Alternatively, in some embodiments, array 810 is disposed outside ofsuch a deposition system. In such embodiments, probes 821 are eachconfigured to direct excitation light 201 onto substrate 203 through arespective window in the deposition system and to receive PL emission202 through the respective window of the deposition system.

In some embodiments, each of probes 821 includes more than a singleoptical fiber for directing excitation light to substrate 203 and/ormore than a single optical fiber for directing PL emission 202 fromsubstrate 203 to PL measurement assembly 830. One such embodiment isillustrated in FIG. 9. FIG. 9 is a schematic cross-sectional view of aprobe 821 of array 810, according to various embodiments of the presentdisclosure. The cross-sectional view of FIG. 9 is taken at section A-Ain FIG. 8. In the embodiment illustrated in FIG. 9, probe 821 includesan emission-receiving fiber 901 and a plurality ofexcitation-light-transmitting fibers 902 arranged aroundemission-receiving fiber 901. In alternative embodiments, probe 821includes multiple emission-receiving fibers 901. Probes 821 can includeany other technically feasible configuration of emission-receivingfibers 901 and excitation-transmitting fibers 902 without exceeding thescope of the present disclosure.

According to various embodiments, an OLED monitoring system candetermine one or more film characteristics of a PL material formed on asubstrate within a system that has deposited the PL material. FIG. 10 isa flow chart of process steps for determining a film characteristic ofthe PL material, according to various embodiments of the disclosure.

A method 1000 begins in step 1001, in which light source 220 generatesexcitation light 201.

In step 1002, one or more components of optical assembly 240 directexcitation light 201 onto PL layer 205 formed on substrate 203, whilesubstrate 203 is disposed in deposition system 290. The one or morecomponents of optical assembly 240 may include free-space opticalelements, fiber-based optical elements, or a combination of both.

In step 1003, in response to excitation light 201 interacting with PLlayer 205, one or more components of optical assembly 240 direct PLemission 202 to detector 230. The one or more components of opticalassembly 240 may include free-space optical elements, fiber-basedoptical elements, or a combination of both.

In step 1004, detector 230 receives PL emission 202. In someembodiments, PL emission 202 includes a transient PL emission thatdecays over time, and in some embodiments, PL emission 202 includes astatic PL emission that has a substantially a constant magnitude overtime.

In step 1005, detector 230 generates a signal based on PL emission 202.In some embodiments, the signal includes static spectral intensityinformation, i.e., a static PL intensity for each of a plurality ofwavelengths or wavelength bands. Alternatively or additionally, in someembodiments, the signal includes static spectral intensity informationfor a specific wavelength or wavelength band. In some embodiments, thesignal includes time decay information of PL emission 202, for examplein response to an excitation pulse from light source 220. In suchembodiments, time decay information can be based on a single wavelengthor wavelength band, or on a plurality of wavelengths or wavelengthbands. In such embodiments, the measurement time is generallysignificantly longer when the time decay information is for each of aplurality of wavelengths or wavelength bands.

In step 1006, computing device 250 receives the signal generated in step1005 from the detector.

In step 1007, computing device 250 determines one or morecharacteristics of PL layer 205 based on the signal received in step1006, such as a thickness of PL layer 205 and/or a dopant concentrationof PL layer 205. As set forth above, in some embodiments, computingdevice 250 can determine a dopant concentration of PL layer 205 basedtime decay information of PL emission 202 in the signal generated bydetector 230. In some embodiments, computing device 250 can determine athickness of PL layer 205 based on a dopant concentration (determinedbased on time decay information of PL emission 202) and on staticspectral intensity information of PL emission 202. In some embodiments,computing device 250 can determine a dopant concentration of PL layer205 based on static spectral intensity information of PL emission 202and thickness information for PL layer 205. For example, the thicknessinformation may be determined via reflectometry or some other techniquethat can be coupled together with the embodiments for PL metrology forOLED layers.

In some embodiments, computing device 250 determines one or morecharacteristics of PL layer 205 based on a plurality of measurements ofPL emission 202, where each measurement is associated with a differentmeasurement location. In such embodiments, computing device 250 canfurther determine a thickness uniformity of PL layer 205 and/or a dopantconcentration uniformity of PL layer 205.

Aspects of the present embodiments may be embodied as a system, methodor computer program product. Accordingly, aspects of the presentdisclosure may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.” Furthermore, aspects of the present disclosure maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. An apparatus, comprising: a light source thatgenerates an excitation light that includes light from the visible ornear-visible spectrum; an optical assembly configured to direct theexcitation light onto a photoluminescent (PL); a detector that isconfigured to receive a PL emission, generated by the PL layer inresponse to the excitation light interacting with the PL layer, andgenerate a signal based on the PL emission; and a computing devicecoupled to the detector and configured to receive the signal from thedetector and determine a characteristic of the PL layer based on thesignal, wherein the characteristic of the PL layer determined by thecomputing device comprises a concentration of a dopant included in thePL layer, wherein the computing device is configured to determine theconcentration of the dopant based on transient PL intensity informationassociated with the PL emission.
 2. The apparatus of claim 1, whereinthe excitation light comprises a first wavelength or group ofwavelengths and the PL emission comprises a second wavelength or groupof wavelengths that is different than the first wavelength or group ofwavelengths.
 3. The apparatus of claim 1, wherein the PL emissionincludes light having a wavelength in the visible spectrum.
 4. Theapparatus of claim 1, wherein the optical assembly includes: anobjective lens configured to direct the excitation light to the PLlayer; and a dichroic mirror configured to direct the excitation lightto the objective lens and to transmit the PL emission.
 5. The apparatusof claim 1, wherein the optical assembly includes a first optic fiberconfigured to direct at least a first portion of the excitation light toa first measuring location on the PL layer.
 6. The apparatus of claim 5,wherein the optical assembly further includes a second optic fiberconfigured to direct a second portion of the excitation light to asecond measuring location on the PL layer.
 7. The apparatus of claim 6,wherein the optical assembly further includes: a third optical fiberthat is configured to direct a first portion of the PL emission to thedetector; and a fourth optical fiber that is configured to direct asecond portion of the PL emission to the detector.
 8. The apparatus ofclaim 6, wherein the optical assembly further includes an opticalsplitter configured to direct the first portion of the excitation lightto the first optical fiber and the second portion of the excitationlight to the second optical fiber.
 9. The apparatus of claim 1, whereinthe detector includes a detector array configured to generate a PLintensity value for each of a plurality of wavelengths, and thecharacteristic of the PL layer determined by the computing deviceincludes a thickness of the PL layer at a specific location on thesubstrate.
 10. The apparatus of claim 1, wherein the detector arraycomprises a linear array.
 11. The apparatus of claim 10, wherein thelinear array is configured to measure the PL emission from multiplelocations on the surface of the substrate that extend from one side ofthe substrate to an opposing side of the substrate.
 12. The apparatus ofclaim 1, wherein the computing device is configured to determine theconcentration of the dopant based on a thickness of the PL layer and astatic PL intensity value of the PL emission.
 13. The apparatus of claim1, wherein the transient PL intensity information includes a decay of PLintensity over time of the PL emission.
 14. The apparatus of claim 1,wherein the computing device is configured to determine theconcentration of the dopant based on a total photon count of the PLemission within a specific range of wavelengths.
 15. A method ofdetermining a characteristic of a photoluminescent (PL) layer that isformed on a substrate disposed in a system for depositing the PL layer,the method comprising: generating an excitation light that includeslight from the visible or near-visible spectrum; receiving a PL emissiongenerated by the PL layer in response to the excitation lightinteracting with the PL layer; generating a signal based on the PLemission; and determining the characteristic of the PL layer based onthe signal, wherein the characteristic of the PL layer comprises aconcentration of a dopant included in the PL layer and is based ontransient PL intensity information associated with the PL emission. 16.The method of claim 15, wherein the excitation light comprises a firstwavelength or group of wavelengths and the PL emission comprises asecond wavelength or group of wavelengths that is different than thefirst wavelength or group of wavelengths.
 17. An apparatus, comprising:a light source that generates an excitation light; an optical assemblyconfigured to direct the excitation light onto a photoluminescent (PL)layer formed on a substrate that is disposed in a system for depositingthe PL layer; a detector that is configured to receive a PL emissiongenerated by the PL layer in response to the excitation lightinteracting with the PL layer, and generate a first signal and a secondsignal, wherein the first signal is based on the PL emission andincludes a decay of PL intensity over time of the PL emission and thesecond signal is based on a total photon count of the PL emission withina specific range of wavelengths; and a computing device coupled to thedetector and configured to: receive the first signal from the detectorand determine a concentration of a dopant in the PL layer based on thefirst signal; and receive the second signal from the detector anddetermine a thickness of the PL layer based on the second signal. 18.The apparatus of claim 17, wherein the detector is configured to receivethe PL emission generated by the PL layer while the substrate isdisposed in a deposition chamber of the system for depositing the PLlayer.
 19. The apparatus of claim 17, wherein the detector is configuredto receive the PL emission generated by the PL layer while the substrateis disposed in a transfer chamber of the system for depositing the PLlayer.
 20. The apparatus of claim 17, wherein the detector is configuredto receive the PL emission generated by the PL layer while the substrateis disposed in an end-of-line chamber of the system for depositing thePL layer.
 21. The method of claim 15, wherein the PL layer comprises anorganic layer.